Solution or lacquer adhesives are bonding compositions which achieve a solid state and resultant strength through evaporation or removal of solvent. This is in contrast to hot melt adhesives which achieve a solid state and resultant strength by cooling from an elevated temperature. In other words, the application of heat melts the hot melt adhesive and after the heat source is removed, it solidifies simply by cooling. Hot melt adhesives are widely used in industrial applications because they can be used to form strong bonds very quickly. However, the difficulty associated with applying hot melt adhesives at elevated temperatures has greatly limited their usage in many applications.
Solution adhesives offer an advantage over hot melt adhesives in that heating is not required in their application to a substrate. Solution adhesives are widely utilized in general purpose and household applications because of their ease of application. Solution adhesives are also the adhesive of choice in a wide variety of industrial applications, such as those where the application of a hot melt adhesive would be difficult or impractical.
Copolyester resins are frequently utilized in solution adhesive compositions. Such solution adhesive compositions are simply prepared by dissolving the copolyester resin in a suitable organic solvent. It is highly desirable for the organic solvent to have a low boiling point. This results in faster rates of solvent evaporation and consequently reduces the time required for bonding. The copolyester resins utilized in solution adhesives commonly contain repeat units which are derived from terephthalic acid and isophthalic acid. Unfortunately, solutions of such copolyester resins form visible haze on standing. Haze formation is, of course, highly undesirable because it renders the solution adhesive composition unsuitable for use in many applications.